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Learn about mouse and keyboard input with the Slick2D game library.

Table of contents

Preface

This module is one in a collection of modules designed to teach you about the anatomy of a game engine.

Although the modules in this collection will concentrate on the Java game library named Slick2D, theconcepts involved and the knowledge that you will gain is applicable to different game engines written in different programming languages as well.

The purpose of this module is to explain some aspects of mouse and keyboard input.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the imagesand listings while you are reading about them.

Figures

  • Figure 1 . Output from the program named Slick0170.java.

Listings

  • Listing 1 . Beginning of the update method.
  • Listing 2 . Test for up or down movement.
  • Listing 3 . Test for collisions with the edges.
  • Listing 4 . Get and save mouse coordinates.
  • Listing 5 . Source code for the program named Slick0170.

Preview

Most games and many simulations are interactive. By that I mean that they require user input to perform according to their design.

I will present and explain a program in this module that allows the user to cause a ladybug sprite (see Figure 1 ) to move inside the game window by pressing the arrow keys on the keyboard or the left and right mousebuttons. (The mouse pointer must be inside the game window for the mouse buttons to move the sprite.)

Figure 1 . Output from the program named Slick0170.java.
Missing image.

Operation

Pressing the right arrow key or the right mouse button causes the sprite to move to the right.

Pressing the left arrow key or the left mouse button causes the sprite to move to the left.

Pressing the up arrow key causes the sprite to move up, and pressing the down arrow key causes the sprite to move down.

The sprite cannot be caused to move up or down (in this program) by pressing mouse buttons.

What you have learned

In the previous module, you learned about using the draw , drawCentered , and drawFlash methods of the Image class.

What you will learn

In this module, you will learn how to use the following methods of the Input class to get input from the user:

  • isKeyDown
  • isMouseButtonDown
  • getMouseX
  • getMouseY

General background information

Modern computer programs fall generally in one or a combination of two categories:

  • Event driven programs
  • Polled programs

Analogy for an event-driven program

I like to think of event-driven programs as being somewhat analogous to the way that we normally drive our cars. When we come to a red stoplight, we removeour foot from the gas pedal, press the brake pedal to stop, and allow the motor to idle, thus consuming minimal fuel. (If we don't have an automatic transmission, we will probably also disengage the clutch and move the gearshiftleaver to the neutral position.)

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Source:  OpenStax, Anatomy of a game engine. OpenStax CNX. Feb 07, 2013 Download for free at https://legacy.cnx.org/content/col11489/1.13
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